Up until the nineteenth century, there was little commercial manufacture of artificial fibers because, with the exception of a crude form of artificial silk, synthetic polymers were largely undiscovered. Fabric was limited to natural fibers like cotton, wool and linen. With the discovery and development of polymers in the early twentieth century, manufactured fibers began to enter the market place in a commercially significant way for the first time. The development of the various fiber manufacturing techniques for polymers, like solvent and extrusion spinning, has taken place in the last fifty years and has developed substantially in that time. Even materials which are difficult to manufacture and make into fiber, such as polyaramids, are now produced on a commercial level to satisfy a global demand. Despite these developments, it is not possible to accurately predict whether a new polymer will make a viable commercial fiber or what type of processing a particular polymer will have to undergo in order to a produce a fiber commercially.
Although there are numerous methods of manufacturing synthetic fiber such as electrospinning, melt spinning, dry spinning and wet spinning, for example, each of these methods of manufacture requires substantively different equipment, different processing conditions and different manufacturing concerns. The three principle methods of producing fiber are melt, dry and wet spinning. All three involve the formation of continuous filament strands by forcing a synthetic material through a circular die. However, melt spinning involves cooling of the subsequent strand to form the solid filament, whereas dry and wet spinning involve the removal of a solvent to form a solid filament. In dry spinning, the solvent evaporates into a gas and in wet spinning the solvent is leached into a liquid bath. It is difficult, if not impossible, to predict which of the various fiber manufacturing processes will produce a commercial fiber, and significantly depends upon the properties of the individual synthetic polymer material to be used to make fiber, i.e., its Tg, melt viscosity, melt index, etc. Each material must be evaluated on its own properties with no predictable guarantee of commercial manufacturing properties.
High melting temperature polymers, such as polyimide polymers having a glass transition temperature that ranges from about 180° C. to about 450° C. have found utility in a variety of applications because of their currently extreme physical properties in addition to their heat resistant properties. For example, Polyetherimides, available from General Electric Company under the ULTEM trademark have high glass transition temperatures, are ductile, flame resistant and generate low amounts of smoke while still having good chemical resistively. These polymers have found wide use in shaped articles, sheet materials, and coatings for use in challenging physical environments such as aerospace applications.
Despite potential use of high heat temperature polymer as fibers and many attempts to produce a polyetherimide fiber, a commercial fiber is not known to have been successfully marketed. U.S. Pat. No. 4,943,481 (1990) to Schilo et al., states at Column 1, lines 7-33:                Heretofore, the synthesis of polyether imide fibers (even of polyimide fibers) by melt spinning, otherwise normal for the production of polymer fibers, was thought unfeasible (cf, for example, “P84—A new synthetic fiber”, Weinrotter, Giesser, published in “Man Made Fiber Yearbook” (1986), 16, page 2408). Polyether imide—but only mixed with other polymers—has only been used for the extrusion of a film (European Patent No. A 160,354).        West German Laid-open Application No. 2,829,811 discloses synthesizing polyether imide fibers by spinning solutions of polyamide acids in an aprotic organic solvent in a spinning bath, after which the freshly spun fibers must be stretched and heat treated to obtain usable textile data.        Polyether imide shapes are also known that are made by injection molding, e.g., spectacle frames, as described in West German Laid-open Application No. 3,429,074. The polyether imide used therein is Ultem® 1000 of General Electric Co. The injection moldability of Ultem 1000 is also mentioned in the Germanlanguage product brochure, “Technische Thermoplaste” (Industrial Thermoplastics), brochure also points out that Ultem® fibers are suitable for making textile fabrics, but no further details are given as to how Ultem® fibers can be synthesized.        
Since the 1990 publication of the '481 patent research on the manufacture of fibers from polyetherimide has continued because despite their high processing temperatures, polyetherimides also have high viscosity at low shear rates such that this class of polymer is a potential candidate for testing for use in commercial fibers. U.S. Pat. No. 5,670,256 to St. Clair et al., discloses polyetherimide fibers made from the reaction product of the monomers 3,4′-ODA and ODPA that is melt extruded in the temperature range of 340° C. and 360° C. to lengths (heights) of 100.5 inches, 209 inches and 364.5 inches. U.S. Pat. No. 5,840,828, to St. Clair et al., discloses a method for making polyimide, and specifically, polyetherimide fibers. Nevertheless, there is no currently known marketed polyetherimide fiber available by any company.
In a conventional system for making polymer fiber, polymer resin is extruded in an extruder and passed through a spinneret containing a plurality of hole openings to form a fiber bundle which is cooled, and drawn to a spool or coil. Polyetherimides require higher processing temperatures not generally used for processing other polymeric fibers. These processing conditions often lead to unexpected and difficult processing issues in the commercial manufacture of articles from polyetherimides.
Oftentimes, for example, the flow through spinneret holes become blocked due to contamination that is present in the system. Particles of sintered metal from Mott filters (i.e., so-called Mott filters in accordance with U.S. Pat. Nos. 3,570,059 and 3,802,821) and other debris that may remain from the filter cleaning operation can be dislodged and carried downstream with the polymer flow where they block one or more spinneret holes. These blocked spinneret holes are known colloquially in the art as “slow-holes” since the polymer flow there through is impeded. When slow-holes occur, the entire spinning line must be shut down in order to prevent the production of off-specification product.
It is therefore desirable to minimize or eliminate complications that negatively effect properties of fibers and productivity in manufacturing the fibers. There is a continuing need in the art to develop processes for new materials being used to make fibers.